嵌套匹配在惯用的 Rust 中是一种不好的做法吗? [英] Are nested matches a bad practice in idiomatic Rust?

问题描述

我有一个 get_url_content 函数并且不关心错误(这只是一个测试).它返回一个 Option.

I have a get_url_content function and don't care about errors (it's just a test). It returns an Option<String>.

extern crate hyper;

use std::io::Read;
use hyper::client::Client;

fn get_url_content(url: &str) -> Option<String> {
    let client = Client::new();
    let mut s = String::new();

    match client.get(url).send() {
        Ok(mut res) => {
            match res.read_to_string(&mut s) {
                Ok(_) => {
                    Some(s)
                },
                Err(_) => {
                    None
                }
            }
        },
        Err(_) => {
            None
        }
    }
}

此功能运行良好，但我发现它不容易阅读.我认为有一些关于这种情况的最佳实践可以使其更具可读性.嵌套匹配是否是一种不好的做法(如 JS 中的回调地狱)，如果是，如何避免?

This function works fine but I find it's not easy to read. I think there are some best practices about this kind of case to make it more readable. Are nested matches a bad practice (like callback hell in JS) and if so, how to avoid it?

推荐答案

让事情更简洁的最简单方法是去掉一些大括号:

The easiest way to make things a bit cleaner is to drop some braces:

match client.get(url).send() {
    Ok(mut res) =>
        match res.read_to_string(&mut s) {
            Ok(_) => Some(s),
            Err(_) => None,
        },
    Err(_) => None,
}

内部匹配可以更简洁地表达为

The inner match can be expressed a little cleaner perhaps as

match client.get(url).send() {
    Ok(mut res) =>
        res.read_to_string(&mut s).ok().map(|_| s),

    Err(_) => None,
}

这建议在外部类型上使用 map(以获得 Result, _>)，然后使用 .unwrap_or 删除结果(无) 或 .unwrap_or_default()

This suggests using a map on the outer type (to get Result<Option<_>, _>) and then dropping the result with .unwrap_or(None) or .unwrap_or_default()

client.get(url).send()
      .map(|mut res| res.read_to_string(&mut s).ok().map(|_| s))
      .unwrap_or(None)

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